Surgical removal of tumors has been one of the conventional treatments for cancer. Such treatment is attended by the high degree of pain and disability, and increased susceptibility to infection which accompanies any surgical procedure. In addition, scarring of tissue inevitably occurs. Due to the substantial disadvantages of surgery, there continues to exist a need for the non-invasive treatment of tumors.
Non-invasive techniques hae been employed in various types of medical protocols. For example, U.S. Pat. Nos. 3,237,623, 3,735,755, and 4,441,486 refer to the use of ultrasound waves to destroy various tissues or cells, and U.S. Pat. No. 4,315,514 refers to the use of selected frequencies of ultrasound to destroy tumor cells. However, because long exposure to ultrasound results in cellular (thermal) degradation, the use of ultrasound waves for the suppression of tumor cells is not favored.
Shock wave technology is currently being used for the non-invasive destruction of human renal and ureteral calcified deposits ("extracorporeal shock wave lithotripsy"). C. Chaussy et al., Lancet, 1:1265 (1980); C. Chaussy et al., J. Urology, 127:417 (1982); E. Schmiedt, C. Chaussy, Urol Int 39:193 (1984). In this technique, HESW are focused by a brass semi-ellipse of high acoustical impedance to a second focal point (F.sub.2).
In contrast to an ultrasonic wave, which consists of sinusoidal wave form, a shock wave consists of a single positive pressure spike with very steep onset and gradual relaxation. While ultrasound can generate pressure waves of approximately 0.1 bar, shock waves can generate pressure amplitudes of up to 1000 bar or more.
Ultrasound is capable of creating a mechanical shock, which is felt at a distance of a few microns. If the ultrasonic wave traveling through a liquid is high enough in amplitude, a microscopic bubble or cavity is produed. This phenomenon, known as cavitation, can produce bubbles of a resonant size which collapse violently to produce high local pressure charges of up to 20,000 atmospheres. For example, at 20 KHz, the resonant bubble size is about 150 microns. H. Alliger, "Ultrasonic Disruption," American Laboratory, (1975).
Shock waves have a greater depth of penetration than ultrasonic waves. Because of this feature, focused shock waves have been used to break up urinary concrements, as discussed briefly above. In those procedures, patients are submergeed in a water-bath and the urinary stone is visualized by the use of two dimensional fluoroscopy. The generated shock wave is propagated through both water and tissue at nearly identical velocities as a result of similar acoustical imedance. However, the target stone, with its high acoustical impedance, is said to absorb and reflect a significant portion of the shock wave. By repeated shock wave exposures in the range of 1000 to 2000 shocks, non-invasive stone disintegration is said to be achieved. The multiple small fragments produced are then said to pass through the intact urinary tract and be excreted in the urine.
Similary, U.S. Pat. No. 3,942,531 refers to the use of shock waves to destroy calcified deposits in the urinary tract. The '531 patent refers to an elliptical container which is applied directly on the skin of the body in an airtight manner. This technique relies on the shock waves' selective attack on the calcified stone, which is said to leave the surrounding tissue intact.
To date, however, there has been no disclosure or investigation of the use of shock waves to destroy or eliminate tissue growth abnormalities such as tumors. On the contrary, clinical use of shock waves, to destory urinary concrements, has been said to be based on the premise that shock waves, meeting with the substantially greater acoustical impedance of the stone, pulverize the stone while "other parts of the body are not affected thereby" ('531 patent, Col. 1 , lines 61-63).